In 10 years, most of New Jersey’s 24 million ash trees in forests — and countless others in neighborhoods, parks and backyards — will be dead.

“It’s dire,” says John Sacco, New Jersey’s State Forester.

New Jersey’s State Forester oversees everything from forest fires, state forests, local tree programs, education programs and forest stewardship to natural areas, forest diseases and rare plants. Now John Sacco has a new challenge.

An invasive insect known as the Emerald Ash Borer, or EAB, is gaining a foothold in this state we’re in after destroying hundreds of millions of ash trees in the Midwest. There’s no stopping the infestation, said Sacco, but it’s possible to save selected ash trees by treating them with an insecticide that kills the Emerald Ash Borer.

As New Jersey’s State Forester, Sacco is working to spread an unpleasant but necessary message: Local governments and homeowners must decide — the sooner the better — which ash trees to save and which to cut down.

In the following interview, Sacco sat down with us to answer questions on what New Jersey residents need to know about this growing problem:

What is the Emerald Ash Borer and where did it come from?

The EAB is a tiny beetle that came from Asia with wood products that were brought to the Great Lakes region. It started showing up in Michigan in the early 2000s and has been spreading ever since.

How does the Emerald Ash Borer kill a tree?

Adult females deposit eggs in bark crevices or under bark flaps on the trunk. After the eggs mature, larvae burrow under the bark and feed on the cambium, which is the water and nutrient transporting layer of the tree. The tree can’t survive without the cambium.

How many trees in New Jersey could the EAB potentially impact?

We have, in our forested lands, about 24 million ash trees. Every one of them will be affected. And that’s not counting the ash trees in our communities and neighborhoods. A lot of our street trees are ash trees. They’re good city trees because they can grow in soils that aren’t well drained and they tolerate soil compaction.

What are the signs that an ash tree is affected by EAB?

The tree just starts looking bad. It starts thinning out at its crown and the leaves start turning yellow. You’ll see shredding bark and woodpecker holes. On the trunk, you may notice D-shaped holes where the insects exit.

Is it possible to save a tree that’s infested with Emerald Ash Borer?

No. If you see a tree that’s in decline, it’s too late. We do not recommend treating a declining ash tree — it’s a waste of money.

What is the New Jersey State Forester’s role in controlling the EAB blight?

We can’t stop it. What we can do is prepare for it and try to get the word out. There are two paths to take: start cutting ash trees down in a systematic manner or start treating them with insecticide. Treatment costs about $200 per tree, and they have to be treated every two years.

Are ash trees being saved in New Jersey’s state parks?

At the state level, we’re concentrating on ash trees in high-use areas like picnic areas, parking lots, historic buildings, playgrounds and places where there are a lot of people walking. We’re treating some but removing others. If it’s a nice tree in a well-used area, we’ll try to keep it.

What about ash trees in New Jersey forests?

There’s not much we can do in the forests except try to save selected populations. In addition to treating the more common ash, we’re trying to preserve a breeding population of pumpkin ash in Monmouth County to keep it viable. We’re also trying to preserve a stand of black ash in Sussex County. Pumpkin and black ash are rare in New Jersey.

If millions of ash trees die in the forests, how will it affect ecology?

Ash has a pretty diffuse distribution in the forests of central and northern New Jersey; it co-exists with other trees. Losing the ash trees will cut down on forest diversity, but there are other trees that will come in to fill the niche. But there’s a danger that invasive plants will grow in the light holes where the ash trees have fallen down.

Is “do nothing” an option in places outside the forests?

Over 99 percent of untreated ash trees in the landscape will eventually become infested and die from EAB, so doing nothing is not a good option for trees planted in yards, near homes, along streets, and in parks, playgrounds and campgrounds.

What can municipalities do to address the EAB blight?

A. The state has funding for Community Forest Management Plans, allowing towns to inventory their trees and manage the treatment of ash trees. But there’s no funding for the actual treatment or removal of trees, so it could be a big budget item for some towns. That’s why it’s so important to start planning now.

To learn more about what you can do about the Emerald Ash Borer, and how to identify ash trees, go to the state’s website at www.emeraldashborer.nj.gov.

And for information about preserving New Jersey’s land and natural resources, visit the New Jersey Conservation Foundation website at www.njconservation.org or contact me at info@njconservation.org.

Michele S. Byers is executive director of the New Jersey Conservation Foundation.